The present invention relates to the field of diagnosis of bodily tissue, and more particularly, to the differentiation of normal from abnormal tissue using laser-induced fluorescence to provide diagnostic information regarding the condition of tissue.
Endoscopic diagnosis is based on the gross morphologic characteristics of tissue, including gastrointestinal and colonic abnormalities, for example. An appraisal of the pathologic condition of many lesions or abnormalities can be made by endoscopic observation alone, but there remains a margin for error that can be substantial for certain types of lesions. Microscopic assessment of biopsy specimens is often considered necessary for many lesions discovered during endoscopy. Furthermore, certain abnormalities of a microscopic nature such as dysplasia in chronic ulcerative colitis or Barrett's esophagus, for example, are usually unrecognizable by gross endoscopic observation.
Of critical concern in the diagnosis of gastrointestinal tissue is the presence and condition of polyps. A polyp of the colon can be defined as any lesion that protrudes above the surface of the surrounding mucosa. See Robbins, S. L., Cotran, R. S. and Kumar, E., Pathogenic Basis of Disease, 1984, pp. 863-869. There are two broad categories of mucosal polyps: Hyperplastic (.about.90%) and adenomatous (.about.10%). Adenomatous polyps are true neoplasms and sometimes harbor areas of carcinoma. Adenomatous polyps can be subdivided into three classes: tubular (.about.75%), tubulovillous (.about.5-15%), and villous (.about.10-15%). There is a general correlation between the type of polyp, and its size and potential for harboring cancer. Hyperplastic polyps are the smallest, tubular adenomas are next in size, and villous adenomas are largest. Hyperplastic polyps are almost always benign. Overall, the incidence of carcinomas in tubular adenomas is about 3-5%. However, somewhere between 25 and 50% of villous adenomas contain carcinomas (See Robbins, supra., at pp. 863-869).
Histologically, hyperplastic polyps are composed of well-formed glands and crypts lined by non-neoplastic epithelial cells, most of which are well differentiated. Tubular adenomas have slender stalks and rounded heads. They are composed of a central core of fibro-vascular tissue and are covered by an epithelium of elongated tubules and glands in which cells are not well differentiated. Marked nuclear hyperchromasia and an increase in the nuclear to cytoplasm ratio are usually present. A range of dysplasia and nuclear atypia is encountered. Villous adenomas are composed of fingerlike pappillae covered by polypoid epithelium. Each papilla is composed of a fibro-vascular core covered by epithelium. Tubular adenomas having between 20-50% villous growth are referred to as tubulo-villous (See Robbins, supra., at pp. 863-869).
In familial multiple polyposis of the colon, the colon is covered by a myriad of neoplastic polyps after the second and third decades of life. The individual polyps are small and mostly tubular. Multiple polyposis inevitably develops into cancer (See Robbins, supra, at pp. 863-869).
Methods have been developed to detect the presence of abnormal or cancerous tissue using laser-induced-fluorescence spectroscopy. Typically, dyes or stains which are known to have a particular fluorescence spectrum and which are selectively retained by the abnormal tissue of interest, or which can be brought directly into contact with that tissue, are used to identify the diseased state of the tissue. More specifically, the emission spectrum produced by the fluorescing dye can be used to locate abnormal tissue within the body and identify its condition.
Laser catheter systems have been developed for the purpose of inserting a light transmitting device into the human body to provide endoscopic examination of the tissue located in front of the catheter. The light emitted by the stained tissue due to the induced fluorescence can be transmitted along the catheter and analyzed at the proximal end of the catheter to produce an emission spectrum for the tissue being illuminated.
Use of dyes or stains for diagnosis has a number of disadvantages. Typically, different tissue types require different materials which must be tested extensively prior to their use in humans. Thus, a need exists for a method and apparatus for not only observing polyps in gastrointestinal tissue but distinguishing between types of polyps without introducing stains or dyes.